[ Zsombor Egri ]
* Add mnemonics support to Action. Fixes LP: #1527527
* Use original Image.source in image extension when no scaling is needed in
order to keep the formatting which would be otherwise removed from a
resolved file URL. Fixes LP: #1401920
* Move UbuntuListView 1.3 code into one single file. Fixes LP: #1523815

[ Albert Astals Cid ]
* Add UCTestExtras::removeTimeConstraintsFromSwipeArea
For that needed to move ucswipearea.cpp from UbuntuComponents to
UbuntuGestures but made it in a private header so we don't have to care much
for the API/ABI stability for now.

[ Tim Peeters ]
* Support scrolling in ListViews with horizontal orientation to the
qquicklistview CPO.
* Add background to AppHeader and remove contents clipping from MainView.
Fixes LP: #1531016, LP: #1531457.
* Hide AppHeader when using AdaptivePageLayout. Fixes bug 1531871.
Fixes LP: #1531871.
* Implement horizontal flicking in the flickable autopilot CPO.
* Re-order to list of pages in the gallery to be alphabetical.
* Fix the autopilot failures introduced with the horizontal scrolling in
the Flickable CPO.
* Update documentation for MainView, Page, AdaptivePageLayout to use the new
PageHeader in all examples. Deprecate old properties. Fixes LP: #1540574
* Add 'animate' property to new internal AppHeaderBase, and do not show a
header anim...